Solar thermal panels can capture solar radiation in the form of heat. An absorber, typically a metal plate or foil coated with a specialized solar absorber or black paint, converts the solar radiation into heat via the process of solar adsorption. The heat can be used directly for space heating, hot water generation, or solar air conditioning. With solar thermal panels, as with any other solar power generation, one of the key determinates of the total output power is the area of the solar panel in terms of square feet or square meters. Typically, the maximum output power is approximately 100 Watts/F2. The larger the panel, the more solar radiation it captures and converts to heat. A 10 F2 panel will generate 100 times the output power of a 1 F2 panel.
Because a solar thermal panel requires both an air gap between glazing and absorber and an air gap between the absorber and insulation, solar thermal panels have used rigid solar glass and a rigid metal support structure to provide these air gaps. As a result, a large solar thermal panel with glass glazing soon weighs too much for economical fabrication, shipping, and installation. Because of weight and size limitations of rigid glass and frame, the largest practical solar thermal panels have been less than 32 square feet and have weighed several hundred pounds at that size. Even with flexible PTFE glazing (U.S. Pat. No. 4,191,169) the panel's rigid frame is heavy and limited in length, restricting panel length to just a few feet. With flexible glazing and an airtight, inflatable design, solar thermal panels can be many times the size at a fraction the weight and cost. A 96 F2 solar thermal panel built with flexible films and foils can weigh less than 100 pounds. Furthermore, by combining high performance materials and manufacturing techniques, a flexible solar thermal panel can equal or surpass the performance of a rigid solar thermal panel. Just a few of these large flexible panels can provide much of the heat required in a residential home for space heating and hot water generation.
There has been the development of flexible solar thermal panels (U.S. Pat. No. 8,191,547 B2; U.S. Pat. No. 4,160,443; U.S. Pat. No. 4,036,209; U.S. Pat. No. 3,908,631) but they have been fabricated using low temperature plastics that employ plastic-to-plastic welding techniques to develop an airtight housing: the outside envelope of the panel is all plastic film. Typically they do not use a high-performance metal absorber because the high temperatures generated would exceed the softening temperature of most plastic films except PTFE. High temperature plastics such as PTFE could be used to provide higher operating temperatures, but because of PTFE's high expense per square foot it would be inefficient and costly to manufacture a solar thermal panel with an entire external PTFE envelope. Furthermore, direct roof mounting on a surface such as asphalt shingles will cause failures in an inflatable panel made solely of plastic films due to the abrasive nature of shingles and the inability of most plastics to withstand long-term abrasion. Minimum installation lifetimes for solar panels should be on the order of 25 years so abrasion is a key failure mechanism. Furthermore, because they are not made from high adsorption metal foils or high optical clarity plastic PTFE films, inflatable solar thermal panel efficiency has been rather low, and does not equal the performance (heat output) of rigid solar thermal panels fabricated from metal and glass.
Another issue with inflatable solar thermal panels is wind resistance. The best location to install a solar panel is on a roof oriented toward the southern horizon (in the Northern hemisphere). A roof installation, however, must be able to withstand wind velocities up to 100 mph in hurricane conditions. To withstand these conditions, a panel should have a minimum profile (vertical height), the ability to be firmly anchored to a roof, and a design that eliminates wind ingress below the panel. The flexible solar panels in prior art do not meet these requirements. In summary, although less expensive to manufacture, inflatable or flexible solar thermal panels have not matched the specifications of rigid solar thermal panels in terms of output power (solar efficiency) or wind resistance.
The use of thin flexible materials permits the fabrication of a solar thermal panel from “roll stock”. Roll stock are thin materials that can be fabricated and then rolled onto a core and shipped in that fashion. Thin aluminum foils and PTFE film glazing are manufactured as a roll material cut to a specified width with hundreds or thousands of feet spooled onto a single roll. Because they are roll stock, they lend themselves to high-volume, high-speed manufacturing processes with highly automated roll stock machinery. In addition, the final product in a roll stock process can also be a roll stock, permitting the fabrication of long solar thermal panels that can be shipped in a “rolled up format”, much like a carpet. The long, airtight solar thermal panel can then “rolled out” and be attached to a series of shorter fixed length support members or wire cable harness at the installation site. Solar panels manufactured as rolls, permit the installation of solar thermal panels in excess of 30 feet or more in length and maximum output power of 7 kilowatts or 24,000 BTUs (British Thermal Units).